The present invention relates generally to a regenerative heat exchange system for transferring heat from one fluid to another and pertains more particularly to a shell and tube system which is capable of transferring heat between electrolytic or corrosive fluids. The present invention is particularly suited for marine use such as in coastal installations, on drilling platforms, or aboard marine vessels where sea water is used as the cooling fluid.
In conventional marine duty heat exchangers, where sea water is used as the cooling fluid, the tube bundles are constructed of copper-alloy tubes and are mounted within a tubular steel shell. Steel inlet and outlet tube sheets are coupled to the inlet and outlet ends, respectively, of the shell by appropriate flanges and are correspondingly apertured to receive and support the ends of the tubes. Cooling seawater passes through the inlet tube sheet and into the tubes, whereupon heat is transferred thereto by recirculating a heated fluid through the shell.
The steel, copper alloy and other materials presently used in the construction of marine duty heat exchangers are heavy and subject to both corrosion and erosion. Copper alloy tubes are particularly subject to erosion at high fluid velocities. Prior art heat exchangers rely on the maintenance of non-turbulent flow conditions to prevent erosion of the tubes and other wetted components. For example, if sea water is pumped through a 3/4" diameter tube at a flow velocity through the center of the tube of approximately 8 ft/sec, laminar flow conditions can be established. Under laminar flow conditions, a thin layer of fluid at the tube walls is maintained at zero velocity, thereby eliminating the problem of erosion.
Unfortunately, however, the same thin layer of fluid at the tube walls which prevents erosion also results in a higher convective resistance and thus impedes heat transfer between the fluids. Since the turbulent flow regimes obtained at fluid velocities of 25 ft/sec or more are required for optimum heat transfer between the fluids, the reduction in erosion achieved by reducing fluid velocity to maintain laminar flow in the tubes comes at the direct expense of heat transfer efficiency.
Another disadvantage of reducing the flow rate of fluid within the pipes is a heightened risk of fouling the sea water side of the inlet tube sheet with biological material. Formations of scale deposits on the inlet side of the heat exchanger are also a problem associated with low flow rates.
It is therefore an object of the present invention to provide an erosion and corrosion resistant heat exchanger apparatus which also provides high transfer efficiency.
It is another object of the present invention to provide a heat exchanger apparatus which can be readily retrofitted into existing installations.
It is yet another object of the present invention to provide a heat exchanger which is resistant to fouling and the formation of scale deposits.
It is still another object of the present invention to provide a method of repairing the tubes within a heat exchanger constructed in accordance with the present invention.
It is also an object of the present invention to eliminate problems caused by tube vibrations at the tube sheets and by temperature gradients within the shell.